The Invention relates to a spring and damper unit according to the preamble of claim 1.
Spring and damper units of this kind are predominantly employed in the motor vehicle technology.
Spring and damper units are known particular through the German printed patent documents DE 3641623, DE 3824932, DE 4334007 and DE 8413300 U1.
In principle such a shock absorbing element comprises a cylindrical casing with the cover and the double acting piston fitted into the casing and having a one-sided piston rod penetrating the cover. The casing on the one hand and the piston rod on the other hand are solidly connected with a body part or, respectively, with the wheel suspension, wherein the free lying part of the piston rod is covered by bellows. For this purpose, the bellows are on the one hand attached to the cover of the casing and on the other hand attached to the head of the piston rod.
The piston subdivides the cylinder space of the casing into a pressure space being reduced during compression and into a pressure space being increased during compression, wherein the two cylinder spaces are connected to the outside through a casing connector to a source of compressed air and are connected to each other by one or several overflow throttles disposed in the piston.
For this purpose simple throttle bore holes are known from the German printed patent document DE 36 41 623, wherein the simple throttle bore holes have the same throttle effect relative to the balancing air stream in both directions of motion, whereby the piston motion is damped to the same extent in two directions. This is disadvantageous since a lesser damping motion is desired during compression relative to the rebound because of the required ground adhesion.
An overflow throttle meeting such a requirement is shown in the German printed patent document DE 84 13 300 U1, wherein the middle throttle bore whole on one side of the piston joins to a ring chamber on the other side of the piston and wherein the throttle bore hole is covered from the ring chamber by a flexible ring disk. This ring disk has on the one hand an outer stop and on the other hand an inner stop such that the ring disk lifts off from the respective stop in one flow passage direction at the outer edge and in the other flow passage direction at the inner edge. Different lever arms result from the different distance of the two stops relative to the middle of the ring disk, wherein the two different lever arms effect a different opening characteristic for the ring disk for the two passage flow directions. It is a disadvantage in connection with this usual kind of overflow throttles, that the ratio of the two opening characteristics with a onetime selected construction is a fixed value and thereby not any longer changeable and adaptable to various application situations.
Spring and damper units are further known from the U.S. Pat. No. 4,844,428, EP 0257779 A3, FR 2705127 A1 and EP 0671572 A1 which exhibit two oppositely directed overflow throttles in the piston for the two pressure spaces. In particular the printed patent document EP 0671572 A1 and the printed patent document FR 2705127 A1 show here overflow throttles, which comprise several uniformly distributed and by sealing disks in a direction closable passage bore holes.
These spring and damper units are complicated in construction and can therefore be produced only with large expenditures. In addition, each of the two flow throttles has a special constructive form, whereby different channel guides and dimensions result. This influences however the opening characteristic of the overflow throttles and thereby the damping behavior of the piston. Therefore these spring and damper units can only be employed for special cases of application.
Therefore it is an object of the present Invention to furnish a spring and damper unit of the recited kind wherein the opening characteristic of the overflow throttle is freely selectable and changeable for each passage flow direction.
This object is achieved by the characterizing features of claim 1. Advantageous embodiments of the Invention result from the features of claims 2 through 7.
The Invention eliminates the recited disadvantages of the state-of-the-art. The separate provision of the overflow throttle is a particular functional advantage. The flow resistance at each overflow throttle and thereby the damping characteristics for each direction of motion can be separately adjusted thereby by changing the sealing disk packets. A functional dependency of the two overflow throttles does not exist. The spring and damper unit is thereby relatively simple and thus cost favorable in construction and in production.